Solar power is an important source of renewable electrical energy. The continuous challenge in the field of solar energy is to develop and manufacture photovoltaic devices having a high efficiency for converting sunlight into electrical energy. The more efficient the photovoltaic device is at performing such a conversion, the greater amount of electricity can be generated for a given investment. While a number of different types of photovoltaic devices have been developed, a particularly suitable photovoltaic device is a thin film semiconductor device having at least one layer, a p-layer, comprising one or more IIB elements and one or more VIA elements from the Periodic Table of Elements. One such photovoltaic device is referred to as a CdTe device because the IIB and VIA elements are cadmium and tellurium, respectively. Typically, these photovoltaic devices also have an n-layer or window layer generally comprising cadmium sulfide. Such a device is sometimes referred to as a CdS/CdTe device or cell. They also typically have a transparent, electrically conductive first contact and a second, generally opaque, electrically conductive second contact. In a usual configuration, these devices have a first transparent conductive layer of conductive metal oxide which is a first electrical contact, an n-layer or window layer of the n-type comprising cadmium sulfide deposited on the first transparent conductive layer, a p-layer deposited on the n-layer and a second, generally opaque electrical contact deposited on the p-layer. The junction of the n-layer and the p-layer is a heterojunction, as is known in the art, and is responsible for the generation of electric potential and electric current when the semiconductor device is exposed to light energy, such as sunlight. Light enters the device from the side of the first transparent layer. Such devices have demonstrated superior efficiency and power generation compared to other types of thin film photovoltaic devices. See for example the article by D. Cunningham et al., “Large Area Apollo Module Performance and Reliability,” 28th IEEE Photovoltaic Specialists Conference, Anchorage, Ak., September 2000. However, while such CdTe thin film, semiconductor photovoltaic devices are efficient and are also amenable to commercial manufacturing methods, the art needs such photovoltaic devices with improved efficiency. The present invention provides for such thin film, semiconductor photovoltaic devices having improved efficiency in converting sunlight into electric current.